A total of 30 percent of the geese included

NandishSS wrote:A total of 30 percent of the geese included in a certain migration study were male. If some of the geese migrated during the study and 20 percent of the migrating geese were male, what was the ratio of the migration rate for the male geese to the migration rate for the female geese? [Migration rate for geese of a certain GMAT = (number of geese of that GMAT migrating) / (total number of geese of that GMAT)]

A. 1/4
B. 7/12
C. 2/3
D. 7/8
E. 8/7

OA:B

Source: GMATPrep EP1

Say the number of geese included in the migration study = x

=> # of male geese = 30% of x = 0.3x
=> # of female geese = 70% of x = 0.7x

Say the number of geese migrated during the study = y

=> # of male geese = 20% of y = 0.2y
=> # of female geese = 80% of y = 0.8y

The migration rate for the male geese = 0.2y / 0.3x = 2y/3x
The migration rate for the female geese = 0.8y / 0.7x = 8y/7x

=> The ratio of the migration rate for the male geese to the migration rate for the female geese = (2y/3x) / (8y/7x) = [spoiler]7/12[/spoiler]

The correct answer: B

Hope this helps!

Relevant book: Manhattan Review GMAT Word Problems Guide

-Jay
_________________
Manhattan Review GMAT Prep

Locations: New York | Beijing | Auckland | Milan | and many more...

Schedule your free consultation with an experienced GMAT Prep Advisor! Click here.

NandishSS wrote:A total of 30 percent of the geese included in a certain migration study were male. If some of the geese migrated during the study and 20 percent of the migrating geese were male, what was the ratio of the migration rate for the male geese to the migration rate for the female geese? [Migration rate for geese of a certain GMAT = (number of geese of that GMAT migrating) / (total number of geese of that GMAT)]

A. 1/4
B. 7/12
C. 2/3
D. 7/8
E. 8/7

We can let t = the total number of geese before migration; thus, the number of male geese = 0.3t and the number of female geese = 0.7t. If we let the number of migrating geese = m, then the number of male migrating geese = 0.2m and the number of female migrating geese = 0.8m.

Thus, the migration rate for the male geese is 0.2m/0.3t = 2m/3t and the migration rate for the female geese is 0.8m/0.7t = 8m/7t.

Thus, the ratio of male migration rate to female migration rate is:

(2m/3t)/(8m/7t) = (7t x 2m)/(3t x 8m) = (14mt)/(24mt) = 14/24 = 7/12.

Answer: B

Hi All,

We're told that 30 percent of a group of geese were male and that SOME of the geese migrated during the study (with 20 percent of that subgroup of migrating geese being male). We're asked for the RATIO of the migration rate for the MALE geese to the migration rate for the FEMALE geese. This question can be solved rather easily by TESTing VALUES (although you have to stay organized and label your work).

Since we're dealing with percents, let's TEST 100.

Total geese = 100
30% are male = 30 male geese
the rest are female = 70 female geese

Some of these 100 geese migrated - and we're told that 20% of this sub-group are male. This means that the number of migrating birds MUST be a multiple of 5. For the sake of continuing to use "round numbers", let's choose 50

50 migrating geese
20% are male = 10 male migrating geese
the rest are female = 40 female migrating geese

We're asked for the RATIO of male migration RATE to female migration RATE

Male rate = 10/30 = 1/3
Female rate = 40/70 = 4/7

(Male rate)/(Female rate) = (1/3)/(4/7) = 7/12

Final Answer: B

GMAT assassins aren't born, they're made,
Rich

NandishSS wrote: ↑

Wed Apr 26, 2017 4:58 am

A total of 30 percent of the geese included in a certain migration study were male. If some of the geese migrated during the study and 20 percent of the migrating geese were male, what was the ratio of the migration rate for the male geese to the migration rate for the female geese? [Migration rate for geese of a certain GMAT = (number of geese of that GMAT migrating) / (total number of geese of that GMAT)]

A. 1/4
B. 7/12
C. 2/3
D. 7/8
E. 8/7

OA:B

Source: GMATPrep EP1

Solution:

We can let t = the total number of geese before migration; thus, the number of male geese = 0.3t, and the number of female geese = 0.7t. If we let the number of migrating geese = m, then the number of male migrating geese = 0.2m and the number of female migrating geese = 0.8m.

Thus, the migration rate for the male geese is 0.2m/0.3t = 2m/3t and the migration rate for the female geese is 0.8m/0.7t = 8m/7t.

Thus, the ratio of male migration rate to female migration rate is:

(2m/3t)/(8m/7t) = (7t x 2m)/(3t x 8m) = (14mt)/(24mt) = 14/24 = 7/12.

Answer: B